1. Filed of the Invention
The present invention relates to a diameter measuring instrument. Although the subject of the present invention can be used to effect all types of measurements, it is primarily intended for measuring the diameter of tree trunks.
2. Description of the Related Art
Forest surveys are normally carried out by measuring a number of trees within a defined area. The diameters of these trees are measured some meter up along respective trunks, with the aid of so called measuring callipers that include two legs or jaws of which one is affixed relative to a straightedge or rule and the other is movable there along. The type of wood is also noted. Such callipers are described, for instance, in Swedish patent specification 0103099-8. These callipers include means for reading the position of the movable leg along the straightedge electronically. When the calliper legs have been moved into abutment with the tree trunk on mutually opposite sides thereof, the measured diameter of the trunk is stored in an electronic memory included in the callipers.
In the case of certain applications it is beneficial to measure the diameter of a tree trunk at a distance up along the trunk. Such a position is immediately beneath a so-called green crown limit on the trunk. The green crown limit is the place where the tree has green twigs all around the trunk. It is also normally desirous to determine the profile or conicity of the trunk. In order to carry out measurements of this nature it is necessary for a person to climb up the tree or up a ladder in order to enable the measurement to be carried out. The measuring process is thus awkward and time consuming.
When measuring, e.g., trees in areas that are not readily accessed or are impenetrable, such as areas in the USA in which the undergrowth is very difficultly forced and can include very thorny bushes among other things, the task of coming close to trees and measuring the diameter of their trunks is both awkward and time consuming.